1. Field of the Invention
The present invention relates to forming Josephson junction devices consisting of superconducting niobium or niobium nitride thin film operating at cryogenic temperatures, and more specifically to such high-performance high-reliability Josephson junction devices that lend themselves to micro-miniaturization of junction patterns without troubles such as micro-short.
2. Description of the Prior Art
In the past, a Josephson junction device of a trilayer structure consisting of, for example, a niobium film as a counterelectrode layer, a surface oxidized layer of aluminum as a tunnel barrier layer and a niobium film as a base electrode layer has been produced, as stated in Japanese Patent Laying-Open No. 58-176983, by forming the base electrode layer, tunnel barrier layer and counterelectrode layer sequentially and then forming a desired pattern of junction and wiring by dry etching. While this method can produce a high-quality contamination-free junction because the junction pattern forming does not intervene in the device forming process, it is often found inconvenient because argon molecules used in the surface cleaning by sputtering method which is carried out after forming the junction pattern on the counterelectrode layer can destroy the tunnel barrier layer through an imperfectly formed insulating layer and further etch the base electrode layer to develop a local micro-short between electrode layer deposition and base electrode layer to the detriment of the junction device reliability.